What is difference between mutex and Futex?

Futex is not mutex Both result in kernel calls, except in one case: The Wait call takes two arguments: one is the address of a user-defined integer variable, the other is the expected value of that variable. If the values don’t match, the call returns immediately.

How is Futex implemented?

A futex consists of a kernelspace wait queue that is attached to an atomic integer in userspace. A properly programmed futex-based lock will not use system calls except when the lock is contended; since most operations do not require arbitration between processes, this will not happen in most cases.

What is the difference between a semaphore and a mutex?

A mutex is an object but semaphore is an integer variable. A mutex object allows multiple process threads to access a single shared resource but only one at a time. On the other hand, semaphore allows multiple process threads to access the finite instance of the resource until available.

Does Pthread mutex use futex?

Specifically in Linux pthread mutexes are implemented as futexes and are therefore fast. Actually, you don’t want to use the futex API itself as it is very hard to use, does not have the appropriate wrapper functions in glibc and requires coding in assembly which would be non portable.

What is the difference between a semaphore and bounded semaphore?

A Semaphore can be released more times than it’s acquired, and that will raise its counter above the starting value. A BoundedSemaphore can’t be raised above the starting value.

What is the difference between a semaphore and bounded semaphore Mcq?

Bounded semaphore holds a counter for the number of release() calls minus the number of acquire() calls, plus an initial value but semaphore doesn’t. A semaphore makes sure its current value doesn’t exceed its initial value while bounded semaphore doesn’t.

What is the difference between mutex and critical section?

From a theoretical perspective, a critical section is a piece of code that must not be run by multiple threads at once because the code accesses shared resources. A mutex is an algorithm (and sometimes the name of a data structure) that is used to protect critical sections.

How are mutexes implemented in Linux?

The mutex subsystem checks and enforces the following rules:

1. Only one task can hold the mutex at a time.
2. Only the owner can unlock the mutex.
3. Multiple unlocks are not permitted.
4. Recursive locking/unlocking is not permitted.
5. A mutex must only be initialized via the API (see below).
6. A task may not exit with a mutex held.

Are mutexes slow?

Thus, mutexes were, in fact, slower than spinlocks in some benchmarks. However, modern mutex implementations avoid all syscalls if there’s no contention. The trick is to make the state of the mutex an enum: unlocked, locked with some waiting threads, locked without waiting threads.

What is bounded semaphore?

A bounded semaphore checks to make sure its current value doesn’t exceed its initial value. If it does, ValueError is raised.